A Linear High-Efficiency Millimeter-Wave CMOS Doherty Radiator Leveraging Multi-Feed On-Antenna Active Load Modulation

This paper presents a Doherty radiator architecture that explores multi-feed antennas to achieve an on-antenna Doherty load modulation network and demonstrates high-speed high-efficiency transmission of wideband modulated signals. On the passive circuits, we exploit the multi-feed antenna concept to realize compact and high-efficiency on-antenna active load modulation for close-to-ideal Doherty operation, on-antenna power combining, and millimeter-wave (mm-Wave) signal radiation. Moreover, we analyze the far-field transmission of the proposed Doherty radiator and demonstrate its wide field of view (FoV). On the active circuits, we employ a gigahertz-bandwidth adaptive biasing at the Doherty auxiliary power amplifier (PA) path to enhance the main/auxiliary Doherty cooperation and appropriate turning-on/-off of the auxiliary path. A proof-ofconcept Doherty radiator implemented in a 45-nm CMOS silicon on insulator (SOI) process over 62-68 GHz exhibits a consistent 1.45×-1.53× PAE enhancement at 6-dB power backoff (PBO) over an idealistic class-B PA with the same PAE at P1 dB. The measured continuous-wave performance at 65 GHz demonstrates 19.4/19.2-dBm PSAT/P1 dBand achieves 27.5%/20.1% PAE at peak/6-dB PBO, respectively. For single-carrier 1 Gsym/s 64quadratic-amplitude modulation (QAM), the Doherty radiator shows average output power of 14.2 dBm with an average 20.2% PAE and -26.7-dB error vector magnitude (EVM) without digital pre-distortion. Consistent EVMs are observed over the entire antenna FoV, demonstrating spatially undistorted transmission and constant Doherty PBO efficiency enhancement.